A. Epidemiology

1. ~1 case per 10,000 per year
2. Peak incidence in their 60s and 70s
3. Infectious Agent
   1. Staphylococcus aureus - most common
   2. Actinomyces - rare
4. 80% posterior, 20% anterior
   1. Most posterior abscesses believed to originate from distant focus of infection
   2. Most anterior abscesses associated with discitis or vertebral osteomyelitis
   3. Also from direct extension from retropharyngeal or retroperitoneal abscesses
5. Thoracic 50%, Lumbar 34%, Cervical 15%

B. Predisposing Factors

1. Immunodeficiency
   1. HIV
   2. Chronic Renal Failure
   3. Diabetes Mellitus
   4. Malignancy
   5. Alcoholism
   6. Intravenous Drug Abuse
2. Spinal Abnormality
   1. Spinal procedure or surgery
   2. Spinal trauma - particularly blunt trauma with initial hemorrhage
3. Local or Systemic Source of Infection
   1. Skin and soft tissue infections
   2. Osteomyelitis
   3. Sepsis
   4. Intravenous Drug Abuse with Bacteremia
   5. Indwelling vascular access (catheters)
   6. Urinary tract infection (with bacteremia)
   7. Nerve acupuncture
   8. Tatooing
   9. Epidural anesthesia or nerve block
4. Bacteria gain access by continuous (~35%) or hematogenous (~50%) spread
5. No predisposing factors or source in ~15%

C. Symptoms [3]

1. Severe low back pain
2. Possible fever
3. Neurologic symptoms
   1. Radiculopathy / paresis
   2. Bladder and/or bowel dysfunction (incontinence)
   3. Plegia
4. Malaise
5. Mental status change
6. Class triad of back pain, fever, and neurologic deficit in only a minority of presentations

D. Diagnosis

1. Rapid diagnosis must be made to avoid permanent neurologic damage
2. Magnetic resonance imaging (MRI) of the spine is recommended diagnostic method
3. Computed tomographic (CT) guided needle aspiration preferred over open biopsy
4. Leukocytosis with left shift (band forms elevated)
5. Highly elevated erythrocyte sedimentation rate (ESR)
6. Local tenderness may be present but is unreliable
7. Staging
   1. Stage 1: back pain at level of affected spine
   2. Stage 2: nerve-root pain radiating from involved spinal area
   3. Stage 3: motor weakness, sensory deficit, bladder and bowel dysfunction
   4. Stage 4: paralysis

E. Treatment

1. Interventional drainage with systemic antibiotics are both required
   1. Surgical decompression was formerly the mainstay of treatment
   2. Percutaneous (CT guided) needle drainage has been successful
2. Endoscopy assisted surgery is also used
3. For medically treated patients, progression is an indication for rapid surgical intervention
4. Outcomes are best when neurological present for <72 hours
5. Antibiotics
   1. In vitro susceptibility must be determined
   2. Vancomycin standard first line for Staph. aureus until sensitivities determined
   3. High dose penicillin G intravenous for Actinomyces
   4. IV antibiotic treatment for 4-8 weeks (6-8 weeks for actinomyces)
   5. Oral treatment generally continued for 6 months for actinomyces
6. ~5% of patients with epidural abscess die, usually due to uncontrolled sepsis or meningitis

F. Good Prognostic Signs

1. Age <60 years
2. Thecal sac compression <50%
3. Neurological cord symptoms <72 hours
4. No comorbid conditions present

References

1. Darouiche RO. 2006. NEJM. 355(19):2012
2. Chao D and Nanda A. 2002. Am Fam Phys. 65(7):1341
3. Lurie JD, Gerber PD, Sox HC. 2000. NEJM. 343(10):723 (Case Discussion)